The focus of this proposal is the link between P53-mediated apoptosis and DNA damage repair, and the possibility of exploiting these pathways to overcome therapy resistance in glioblastoma. This tumor is characterized by an unusually malignant nature, by frequent P53 mutation (50% overall) and by high resistance to all forms of presently available therapy. We have found that glioblastoma cells expressing endogenous mutant P53 become much more sensitive to cisplatin and radiation-induced apoptosis following gene transfer of wild-type P53, even under conditions where overall growth of the cells is not significantly changed. In light of the potential clinical interest of this observation for glioblastoma, the project will address: (1) the generality of the sensitization effect in vitro with respect to different P53 mutations, including those which act as dominant-negatives, and with respect to different drugs, (2) The role of DNA-mediated suppression. In particular, we will explore a novel approach to therapy sensitization using P53 along with inhibitors of the AP-1 transcription factor which regulates expression of several DNA repair enzymes. The combined effects will be examined of P53 with each of two AP-1 inhibitors, a dominant-negative inhibitor of c-jun (mutant jun) that inhibits the phosphorylation-rated functions a AP-1 associated with cellular transformation, and the synthetic retinoid, SR11220, capable of down-regulating AP-1 activity, (3) The specific components of DNA repair that affect P53-mediated suppression, (4) The in vivo application of P53 combination approaches using a subcutaneous nude mouse model and a fisher rat intracranial model of glioblastoma. These studies are designed to provide a rigorous pre-clinical evaluation of P53-mediated growth suppression and therapy sensitization, and to fully explore the combine potential of P53 and ap-1 inhibitors, as potential second generation anti-cancer agents with specificity for tumor cells. The studies will also provide insight into the fundamental nature of drug and radiation resistance in glioblastoma.